With the rapid development of enterprise data communication services, residential area broadband access services, and related convergence services, Ethernet is applied in a broader range. The number of Ethernet devices is increased greatly whose network locations cover the high-end, the intermediate-end, and the low-end. With wide applications of the Ethernet devices, subscribers put more emphasis on device reliability, and pose higher requirements for protecting Ethernet ports.
For the Ethernet ports, an over-voltage of network cable induction is mainly in a common-mode. Hence, a current ordinary protection circuit is as shown in FIG. 1. An Ethernet interface circuit includes a transformer unit and a network port (RJ45 interface) that are connected with an Ethernet chip. Signal lines 1 and 2 of the network port are electrically connected with a receiving terminal of the transformer unit, signal lines 3 and 6 are connected with a sending terminal of the transformer unit, and signal lines 4, 5, 7, and 8 are idle. An over-voltage of the signal lines 1, 2, 3, and 6 of the network port (RJ45 interface) is discharged through a gas discharge tube connected with a center tap of the transformer unit, and the idle signal lines 4, 5, 7, and 8 of the network port are connected with a Bob-smith circuit to withstand an over-voltage through insulation and withstand voltage.
In a process of implementing the present invention, the inventor finds that the prior art at least has the following problems.
When a surge voltage is higher, the over-voltage on the signal lines 1, 2, 3, and 6 is changed to a low voltage by clamping of the gas discharge tube connected with the center tap of the transformer, while the signal lines 4, 5, 7, and 8 withstanding the over-voltage through the insulation and withstand voltage are still at a high voltage. At this time, the signal lines 4, 5, 7, and 8 discharge to the signal lines 1, 2, 3, and 6 at a modular plug of an RJ45 connector. As shown in FIG. 2, the signal lines 5 and 7 discharge to the signal line 6, which causes a common-mode over-voltage in a large magnitude to convert into a differential mode over-voltage, so as to damage the Ethernet chip. That is to say, a problem of damaging the Ethernet chip since the common-mode over-voltage is converted into the differential mode over-voltage due to potential difference between the signal lines 1, 2, 3, and 6 and the signal lines 4, 5, 7, and 8 exists in a current Ethernet port protection circuit.